Refrigerated display merchandisers (also referred to as display cases) are used to contemporaneously refrigerate and display products in commercial settings such as supermarkets, mini-marts and convenience stores. There are two general categories of display cases: those with an open front display and those with a closed front display. Open front type display cases are advantageous in that unlike closed front type cases they do not have containment doors, and thus they allow for unobstructed display of products and enable consumers to handle products without the inconvenience that occurs when it is necessary to open a door to access products in a closed type case. However, both types of display cases are used today and will likely continued to be used for the foreseeable future.
Although the specific design and arrangement of open and closed front display cases can vary, current models include a heat exchanger (e.g., an evaporator), which serves an important role in maintaining a product display region at a proper temperature to prevent spoilage of displayed products. The evaporator operates in a cycle during which air is circulated over the evaporator, cooled by refrigerant within the evaporator, and then directed to the product display region of the display case so as to cool the products therein. At least a portion of the cooled air also forms an air curtain in the front of the display case and thus acts as a barrier to inhibit warm air from entering the product display region. Some of the air from the air curtain is merged with air from the product display region and is drawn back into the evaporator, thus restarting the air cooling cycle anew.
A wide variety of evaporator designs are incorporated or are possible for application in refrigerated display merchandisers. Among these are so-called microchannel evaporators (also often designated by the abbreviation “MCHX”), which refer to a particular type of heat exchanger that includes substantially parallel flat tubes with fins disposed between and connected to the tubes. Of late, microchannel evaporators are receiving an increasing amount of attention from the Heating Ventilating Air Conditioning and Refrigeration (HVACR) industry due to their oftentimes superior performance in certain settings (e.g., in refrigerated display merchandisers) as compared to evaporators that have different designs, such as round tube plate fin evaporators.
During operation of a microchannel evaporator, moisture in the air that enters and exits the microchannel evaporator will condense on the surfaces of the tubes and fins when their surface temperature is at or below the dewpoint of the air. Thus, when the microchannel evaporator is maintained at a freezing temperature, moisture will condense on the surfaces of the tubes and fins as frost, which, if not removed, can cause problems such as increased product temperature and decreased efficiency of the microchannel evaporator. If, instead, the microchannel evaporator is operated at an above-freezing temperature, then moisture will condense on the surfaces of the tubes and fins as water, which, if not adequately drained, will disadvantageously impede the flow of air through the microchannel evaporator.
Various options exist for removing the frost from (i.e., for defrosting) a microchannel evaporator. If the microchannel evaporator utilizes a medium temperature (e.g., about 15° to about 30° F.) refrigerant, then the flow of refrigerant to the microchannel evaporator can be halted temporarily (e.g., for about 20 to 30 minutes) at predetermined intervals (e.g., 4 to 6 times within a 24 hour period) while one or more air circulation devices (e.g., fans) present within the display case continue to operate. If, however, the microchannel evaporator uses a low temperature refrigerant (e.g., about −5° F. to about −40° F.), then halting the flow of refrigerant alone is not sufficient to melt the frost. Instead, the microchannel evaporator can be equipped with a heater, and/or hot gas from the compressor can be introduced into the microchannel evaporator to melt the accumulated frost.
Although these techniques successfully cause the frost on a microchannel evaporator to thaw and melt (i.e., to defrost) without also causing the temperature of the display case and its contents to rise to an unacceptable level, a problem arises in that a portion of the melted frost condensate is retained on the surfaces of the tubes and fins of the microchannel evaporator and refreezes once refrigerant flow resumes. This problem is particularly troublesome since any frozen condensate that remains following defrosting will disadvantageously impede the flow of air through the microchannel evaporator during a cooling cycle. Although this problem could be addressed through longer and/or more frequent defrost periods, that, in turn, would increase the temperature of the display case and its contents to unacceptable levels during the defrost cycle(s).
Some in the art have attempted to solve this problem by orienting microchannel evaporators in a manner that purportedly promotes reliable removal of melted frost condensate from the surfaces of the tubes and fins of the microchannel evaporator, as well as continuous removal of condensate from the surfaces of the tubes and fins of the microchannel evaporator during non-freezing applications. Two such approaches are illustrated schematically in FIGS. 1-1C and FIGS. 2-2C.
FIG. 1 depicts a microchannel evaporator 10 that rests atop a horizontal surface 25 and includes a plurality of fins 20 connected to a plurality of tubes 30. As shown in FIG. 1A, the fins 20 (only one fin is shown for ease of viewing) of the microchannel evaporator 10 are disposed in a vertical plane with respect to a vertical axis 50 of the display case (not shown) in which the microchannel evaporator is present. Conversely, the tubes 30 to which the fins 20 are connected are disposed in a horizontal plane with respect to the vertical axis 50 of the display case. As illustrated by FIGS. 1B and 1C, and in an effort to promote removal of condensate from its fins 20 and tubes 30, the microchannel evaporator 10 can be oriented so as to be offset with respect to the vertical axis 50 of the display case by an angle, A, of up to 30° to the left (see FIG. 1B) or up to 30° the right (see FIG. 1C). That, in turn, renders the fins 20 substantially vertically disposed with respect to the vertical axis 50 of the display case, and the tubes 30 substantially horizontally disposed with respect to the vertical axis of the display case.
Referring again to FIG. 1A, arrows 70, 80 depict the flow path of condensate when present on fins 20 and tubes 30 that are oriented as depicted in FIGS. 1-1C, wherein arrows 70 depict the flow path of condensate on the fins 20 and arrows 80 depict the flow path of condensate on the tubes 30. As indicated by arrows 80, a horizontal orientation (see FIG. 1A) or a substantially horizontal orientation (see FIGS. 1B and 1C) of the tubes 30 with respect to the vertical axis 50 of the display case will cause at least a portion of the condensate to pool on the surfaces of the tubes 30 and between adjacent fins 20 rather than be removed therefrom. This is problematic because the pooled condensate will tend to refreeze and cause the above-noted air flow problems if the microchannel evaporator 10 of FIGS. 1-1C is being used in a medium or low temperature freezing application. Also as explained above, the pooled condensate can cause air flow problems even if, instead, the microchannel evaporator 10 of FIGS. 1-1C is being used in an above-freezing application.
FIGS. 2-2C illustrate an alternative orientation for a microchannel evaporator 10′ in which the microchannel evaporator 10′ also rests atop a horizontal surface 25 and includes a plurality of fins 20 connected to a plurality of tubes 30. In this instance, however, and as best shown by the more detailed view of FIG. 2A, the tubes 30 of the microchannel evaporator 10′ are disposed in a vertical plane with respect to the vertical axis 50 of the display case (not shown) in which the microchannel evaporator 10′ is disposed, whereas the fins 20 (only one fin is shown for ease of viewing) of the microchannel evaporator 10′ are disposed in a horizontal plane with respect to the vertical axis 50 of the display case.
As illustrated by FIGS. 2B and 2C, and also in an effort to promote removal of condensate from its fins 20 and tubes 30, the microchannel evaporator 10′ can be oriented so as to be offset with respect to the vertical axis 50 of the display case by an angle, B, of up to 30° to the left (see FIG. 1B) or of up to 30° the right (see FIG. 1C). That, in turn, renders the fins 20 substantially horizontally disposed with respect to the vertical axis 50 of the display case, and the tubes 30 substantially horizontally disposed with respect to the vertical axis of the display case.
Referring again to FIG. 2A, arrows 70, 80 depict the flow path of condensate when present on fins 20 and tubes 30A, 30B that are oriented as shown in FIGS. 2-2C, wherein arrows 70 depict the flow path of condensate on the fins 20 and arrows 80 depict the flow path of condensate on the tubes 30. As indicated by arrows 70, 80, a horizontal (see FIG. 2A) or a substantially horizontal (see FIGS. 2B and 2C) orientation of the fins 20 with respect to the vertical axis of the display case will cause at least a portion of the condensate to pool on the surfaces of the fins rather than be removed therefrom. This is problematic because, just as was the case with the FIGS. 1-1C microchannel evaporator 10, the pooled condensate on the FIGS. 2-2C microchannel evaporator 10′ can cause the above-noted air flow problems if the microchannel evaporator 10′ of FIGS. 2-2C is being used in an above-freezing application, or in a low or medium temperature freezing application.
Further, due to the orientation of the fins 20 and tubes 30 of the FIGS. 2-2C microchannel evaporator 10 ° with respect to the vertical axis 50 of the display case, it becomes necessary to deliver refrigerant to the microchannel evaporator 10′ via an inlet header (not shown) that is generally longer than that which is used for the FIGS. 1-1C microchannel evaporator 10. In fact, in some instances, the inlet header that is used for a microchannel evaporator 10′ oriented as shown in FIGS. 2-2C can be upwards of 10 feet in length. That alone can pose design and/or manufacturing difficulties, but perhaps more problematic is it necessitates that refrigerant travel multiple feet through the inlet header to reach the microchannel evaporator 10′. As such, there is a comparatively much greater risk of separation of the liquid and vapor components of the refrigerant within the inlet header than there would be if the inlet header was instead shorter as it would be for the FIGS. 1-1C microchannel evaporator 10. Moreover, if liquid/vapor separation was to occur, not all tubes 30 of the FIGS. 2-2C microchannel evaporator 10′ would be guaranteed to receive refrigerant, and, consequently, the microchannel evaporator 10′ of FIGS. 2-2C could produce comparatively warmer air than expected. This warmer air would not as fully cool the display case, which in turn, might not be able to function effectively, let alone optimally. This would present a problem whether or not the microchannel evaporator was being used in an above-freezing application, or in a low or medium temperature freezing application.
Therefore, a need presently exists for a refrigerated display merchandiser that includes a microchannel evaporator which can be oriented so as to effectively remove or cause to be removed condensate that accumulates on the surfaces of the tubes and fins of the microchannel evaporator during its operation, yet that also will not necessitate a lengthy refrigerant inlet header and will not otherwise interfere with the operation, functioning and/or design of either an open type or a closed type of refrigerated display merchandiser in which the microchannel evaporator is incorporated.